1. Field of the Invention
This invention relates to sheet registration mechanisms for selectively registering sheets being moved seriatim in a reproduction apparatus such as a copier or printer.
2. Description Relative to the Prior Art
Reproduction apparatus such as copiers and printers are known for making copies of an original document or image on individual sheets or substrates. The substrates or sheets are either cut from a continuous supply thereof into desired sizes, or are precut and stored in a hopper for such use. In either case, the individual sheets or substrates are fed seriatim along a sheet travel path for receiving a toner image from a moving image bearing surface for example of an imaging web or drum. Since the image bearing web or drum is moving relative to the moving individual sheet or substrate, the movement of such sheet or substrate must be synchronized and coordinated with the movement of the web or drum in order to insure correct and acceptable registration of the toner image with the sheet or substrate.
3. Description Relative to the Prior Art
For registering the sheet or substrate to the toner image, various types of sheet registration mechanisms are well known including for example those having means for buckling the sheet during such registration. Examples of the latter are disclosed in U.S. Pat. No. 3,957,366 issued May 18, 1976 to Taylor et al., No. 4,135,804 issued Jan. 23, 1979 to Schoppe et al., and No. 4,669,853 issued Jun. 2, 1987 to Sosinski et al. In these types of buckling registration mechanisms, the lead edge of the sheet to be registered is fed by first sheet feeding means along a sheet path against a releasable stop member that is mounted less than the intrack dimension of the sheet from the first sheet feeding means. The stop member is suitable for stopping and aligning such lead edge. Continued feeding of the sheet after the lead edge is stopped then causes the sheet to buckle against the stop member and into an open buckling area which adjoins and opens from one surface of the sheet path. The stop member typically is positioned immediately upstream of a second sheet feeding means which then feeds the registered sheet following a timed and registered release of such sheet by the stop member.
Although buckling of the sheet as above is intended to prevent skewing of the sheet when fed by the second feeding means, significant skewing however at times still occurs, particularly at the second or downstream sheet feeding means. Such significant skewing causes parts of some of the sheets to bend and fold noticeably in a substantially transverse direction to the direction of sheet travel. Such bending and folding results in undesirable wrinkling of the sheet as the sheet is being fed by the second or post registration sheet feeding means.